Capacitor is a system consisting of two
conductors having equal and opposite charges separated by an insulator (insulating medium) or dielectric. The electric field in the region between two conductors is proportional to magnitude of electric charge. Besides, the potential difference between two conductors is proportional to the magnitude of charge Q.
The capacitance of a capacitor is the ratio of magnitude of charge on either of conductors to the magnitude of potential difference between two conductors.
C = Q/V. …(12.45)
The ability of a conductor to store an electric charge and electrical potential energy is called capacitance of the capacitor. The word condenser is used sometimes and which is a misnomer, as the capacitor does not condense energy as such, but it stores energy.
Capacitor has many applications such as,
(1) tuning in radio circuit.
(2) for smoothing rectified current in power Suppliers.
(3) for eliminating sparking of points, when they are open or close in an ignition system of automobile engine.
(4) for storage of large amount of charge for use in nuclear reactors.
The SI unit of capacitance is farad, in honour of Michael Faraday.
1 farad = 1coulomb / 1volt
1F = 1 C / 1V
A capacitor has a capacitance of one farad, if the potential difference across it rises by 1 volt, when 1 coulomb of charge is given to it.
IuF=10^-6 F, 1nF= 10^-9F, 1pF= 10^-12F.